1. Field of the Invention
The present invention is directed to a method and architecture for providing redundant SS7 signaling control in a packet voice network environment (e.g., a Voice over IP environment).
2. Discussion of the Background
SS7 is a reliable and widely used protocol in the circuit switched PSTN world for managing telephone calls (e.g. setting up & tearing down a call on a particular voice channel or circuit). SS7 networks often include STPs (Signal Transfer Points), which are fast & efficient switches for SS7 packets. Then, SS7 signaling forms a separate physical network from the voice circuits for passing signaling information. Compared to in-band signaling (e.g., CAS MF), SS7 is much faster, reduces fraud, and enables adding value-added services. The switches terminate voice trunks or circuits and telephone lines, and connect to the SS7 network by connecting to a “home” STP pair through signaling links known as A-links. Examples of switches used in the PSTN include 5ESS from Lucent & DMS500 from Nortel.
For detailed specifications on the SS7 standards, readers are referred to the American and International standards: ANSI T1.111, ANSI T1.113, Telcordia GR-246, ITU-T Q.7xx series. Each of those standards is incorporated herein by reference in its entirety.
FIG. 1 is a general functional diagram representing an exemplary SS7 network. As shown in FIG. 1, the switches terminate voice circuits that are controlled through the signaling messages flowing over the signaling network. A switch is located in a central office. By way of example, if switch A fails (or gets destroyed, for example, by an earthquake), all the voice circuits controlled by the switch become unusable (even if the controlled circuits were terminated to a remote location box that is slave to the switch A's controlling CPUs). That is how SS7 is deployed today.
Known voice over IP (VoIP) networks use other signaling protocols for call connection within the IP environment. Examples of these signaling protocols are Media Gateway Control Protocol (MGCP) described in IETF standard RFC 2705, MEGACO protocol described in IETF standard RFC 2805, Session Initiation Protocol (SIP) described in IETF standard RFC 2543, and ITU-T H.323 protocol suite. However, often calls originate from a caller and terminate to a callee in the circuit switched PSTN. Therefore, VoIP networks may have to connect to the PSTN for call origination and/or termination. Although VoIP networks have the choice to use CAS (Channel Associated Signaling) or ISDN signaling, SS7 should be the signaling of choice to connect to the PSTN because of the advantages SS7 brings.
Similar to the SS7 deployment in the circuit switched environment case mentioned previously, if all SS7 signaling links to a VoIP network switch (termed as Softswitch (SSC)) fails, then all the voice circuits controlled by the switch become unusable.